In the scintillators used in a variety of radiation detectors or sensors, there have mainly been used single crystalline materials. In particular, the γ-ray detector requires the use of a large-scale single crystal having a high density and constituted by heavy elements. In addition, such a single crystal should have a high emission or luminous strength and the wavelength of the light emitted from the single crystal should likewise be adapted to the highly sensitive range of the optical detector. For this reason, there has presently been used the single crystal of cerium (3+)-added gadolinium (3+) orthosilicate (cerium-activated Gd2SiO5, commonly referred to as “GSO”) as the most excellent material for such a scintillator.
However, the GSO single crystal has a strong crystalline anisotropy, the production thereof requires the use of a technology of a high order and therefore, the resulting single crystalline material is quite expensive. On the other hand, various kinds of fluorescent substances have been used in other applications, but there has been desired for the development of a fluorescent substance excellent in processability other than single crystalline ones and there has also been desired for the development of a fluorescent substance, having a good luminous efficiency from the viewpoint of the reduction of the electric power consumption of a variety of devices.
For instance, Japanese Un-Examined Patent Publication 2001-282153 discloses a method for the preparation of UV fluorescent glass containing a rare earth element-containing oxide, but the glass comprises CeO2 as a fluorescent component and this article does not disclose, at all, a fluorescent substance represented by the general formula: (A1−xBx)2Si2O7.
In addition, there is disclosed, in S. W. Lu et al., J. Phys. Chem. Solids, 2001, 62:777–781, a method for the preparation of Mn2+-activated Zn2SiO4 powder, but this article does not disclose such a fluorescent substance represented by the general formula: (A1−xBx)2Si2O7.